PROJECT SUMMARY/ABSTRACT Despite decades of intervention efforts, dental caries remains the most prevalent chronic disease in humans. Streptococcus mutans, the primary causative organism of caries, exhibits a variety of virulence factors that are quorum sensing (QS)-dependent. Surprisingly, the addition of exogenous Com QS signaling peptide, CSP (eCSP) at higher than physiological concentrations results in competence-induced cell death in S. mutans cultures, which represents the potential to be developed as a novel therapeutic strategy to control S. mutans populations. Although the Com signalling pathway and eCSP-induced cell death in S. mutans have been documented in studies in vitro using established laboratory strains, the influence of environmental factors in the oral cavity on these phenomena has not been determined. We have demonstrated that other oral bacteria attenuate some of the QS-mediated virulence activities such as biofilm formation, bacteriocin production, antimicrobial resistance, and genetic competence in S. mutans by inactivating the CSP. In addition, S. mutans is persistently competent in biofilms, whereas it has only a short window of competence in broth cultures, which indicates that growth conditions have impact on pheromone responses in S. mutans. Therefore, determination of influences of oral environmental factors such as bacterial interactions in dental plaque and encounters with other antimicrobial agents (either exogenously applied or endogenously present in saliva) on eCSP- induced S. mutans cell death is crucial for the development of eCSP as a novel class of antimicrobials for caries prevention. This application aims to prove our hypothesis that overstimulation of QS by eCSP affects viability and population dynamics of S. mutans in conditions mimicking the pathogen's existence in the oral cavity. We will determine if eCSP induces cell death of S. mutans in multispecies biofilms and in the presence of saliva. We will also assess the influence of eCSP on S. mutans' susceptibility to other antimicrobials. In addition, the efficacy of eCSP in causing S. mutans autolysis in caries lesions on extracted teeth will be assessed. Since all of S. mutans strains up to date exhibit the same sequence of CSP and S. mutans eCSP does not induce cell death in other oral species we have tested, this approach is expected to be highly specific for eliminating S. mutans, without disturbing host-microbial homeostasis. Indeed, our long-term goal is to use this strategy (selectively targeting a pathogen without disturbing host and microbial homeostasis) to attenuate S. mutans persistence and thereby reduce dental caries.